Electromagnetic pick-up device for phonographic records



' Dec. 30, 1930.

L. THOMPSON ELECTROMAGNETIC PICK-UP DEVICE FOR PHONOGRAPHIC RECORDS Filed Jan. 7, 1930 INVENTOR L/NfOLN THOMPSON BY v I r z f 5 ATTORNEY Patented Dec. 30, 1930 TE'S,

PATENT Pica FLINCOLN THOMPSON, F NAUGATUCK, CONNECTICUT, ASSIGNOR TO WM. H. BRISTOL TALKINGPICT'URE CORPORATION, OF OF CONNECTICUT I WATERIBURY, CONN ECTZCUT, A CORPORATION.

Application filed Jamie-y 7, 1930. Serial No. 419,009.

The invention relates to apparatus utilized in the reproduction of sound; and more especiallyto. an electricaltransmitter unit for .use with phonographic records of the lateral cut type, the grooves of which are adapted to impart. an oscillatory movement to a stylus member operating therein.

' 'It has for its object certain improvements in a pick-up device of the nature set forth in a prior U. S. Patent, No. 1,637,165,granted to me and Joseph B. Marshall, as assi nors to The Bristol Company. In this sai patent there is disclosed a torsionally secured reed "member which. extends through, a trans mitter coil" and air gap between the pole pieces of a magnet, said reed being adapted for vibration by a stylus to cause electric currents to be generated within the said 0011.

Such currents, being usually of insufficient magnitude to operate the ordinaryexisting receiver devices with the desired yolume, are generally amplified to the requ red extent by any of. the well-known exped1ents.

The said improvements involved in the novel pick-up device contemplatea support of a disk-like nature for the reed and stylus holder rather than a shaft support, as in the earlier embodiment; and, furthermore, a sealed casingfor the said reed to contain a suitable damping liquid therefor, the said disk not only affording the torsional support for the reed but serving to seal off,

connection. 7

This is conveniently effected by providing, for example, a circular outlet in the also, the casing at the reed and stylus holder bottom of the casing retaining the magnet and transmitting coil of the pick-up; and

mounting over said opening a flexible disk secured rigidly at its circumference to the 1 casing, said disk having projecting centrally therefrom into the casing and through the transmitting coil and between the pole pieces a reed of soft iron, while from the opposite face of the disk projects outwardly a stylus holder fixedly secured eccentrically thereto. Oil or other liquid of suitable consistency is retained by the casing so as to entirely immerse the pole pieces, transmitting coil and reed therein, and thus serving to damp the vibrating parts and eliminate the effect of natural frequencies of the same. Moreover, an outlet for the conductors from the transmittin coil is provided in the casing, and is also suitably sealed to prevent leakage therefrom, while a filling opening with removable plug is arranged in the casing to admit the damping liquid into its interior.

The nature of the invention, however, will best be understood when described in connection with the, accompany drawings, in which:

Fig. 1 is a side elevation of the novel pickup device and mounting therefor, and shows also a stylus of said device in engagement with a phonographic record. 7 7

Fig. 2 is a front elevation of the pick-up device, with cover plate broken away to disclose the interior.

Fig. 3 is an underneath view.

Fig. 4.- is a transverse vertical section through the pick-up device.

Fig. 5 is a front elevation of the reed, stylus holder and supporting diaphragm.

Fig. 6 is a plan thereof.

Referring to the drawings, the novel pickup device is arranged to be mounted in any suitable manner for floating over the top of the phonographic record 10 of the Wellknown lateral-cut, disk type and arranged to be carried by a turn-table 11 by which it may be rotated in manner well understood. Any suitable means for thus supporting the pickup device with reference to the turn-table and record thereon may be utilized; and in the drawings there is indicated a standard or base 12 of substantial proportions, the same having a socket 13 which is designed to receivea forked pin 14 for rotation therein so thatt-he pick-up device may be caused to swing freely in a horizontal plane. The latter'is designed, also, to be carried for this purpose by an arm 15, preferably in the form of a tube through. which the outgoing leads or conductors 16 may be brought for connecting the pick-up device with the external circuits and apparatus (not shown). The pickup end of the arm 15, moreover, is adapted. to

e lllQlPllIPD-SQ of retaining ,ajsuitableadan this arm is pivotally secured to the upper end "of pin 14 toprovide for a universal joint Which pin; for this purpose. te nnates in a. bifurcated portien iii havi 1v l rested studs20 upon which tnejarni 15 1: roekin a vertical plane as in insertn stylus 21 of thepicleup member in the grooves of the record 10 and removing the same there- "fi H i i 1 The picsi upnieniher comp 7 a'conductor outlet 26 through the hack of said casing and an opening 2? in the bot-'- tom thereof, Whilea removable plate'28' is i "ron't oftheieasing. Aplug Wion seals the outlet 26 and has a 29 oii Y pair oi ralpo a fO extendingltherd throue' .i'v'nnethe ope 111g filis adapted to'be close-(h as hereinafter setforth 'so that I the :e?

releasing heeoines sealed thereby for liquid'snch as aheavy' oil. 7

--Vl lth1n the casing, furthermore-fie mounted a magnetized memberBlQpreiferahly of ends of niagnetrest'upon the bottom of the casing at either s deof the opening therethrough and" have attached thereto pole 7 dlyldireeted over the opening 335 and 34 respectively The-said plates provide an intermediate recess in "the'po'les for repiecesia 27 with upper andloweripairs"of .plates between them an annular bobbin or the conductors 1.6. v

The passageway 35 throughthe hololoin is rectangular in cross-section and TGQlS JGIfS 'tl1 e g:-air of lowerpla'tes so "that a through j passageway into the interior of the casing is z-iii'orded by inher or J- r so the ling 42 am the opening 2'? centered there- ,d over the thereof and extending at right angles there to to receive and hold the stylus :21. v i

' t will be observed that the said holder and reed eonstitutean integral unit with the said disk which. serves the double purpose of at- Eerding a torsional support fQPtASZlGGCl rel atively to the magnetized and transmitting ts and to seal the easing so that the *swithin the same may be immersed other sfitable' liquid i0 damp the foratin'e' parts and eliminatetheleffect' of itural rrequencies of suchparts. 1

To admit of eon Venient'filling of the casing with such damping liquid, a filling opening 47 "may bearranged'in the casing Wall and *norinell y closed by a removable plug 48;: In themenutacture ot-the novel pick-up device,

the U or liors shel-a magnettypeq and also -preferahlt permanently magnetized. The,

mherrnoi'e; the same is assembled AVlt the oil-tight surfaces preferably shellacke'd, $3 110.

the unitis thenbaked" with the filling plug igemoved, ;-Whereupon the oll or other idamping liquid is introduced through the fillirig opening H and the plugldreturnedto seal the 'casing.

Normally, said dislcmaintains thereed in its neutral position substantially midway of the airgg'a J-s; hut WllGILtllHStjilHSi operates 'in thegrooves-o f the-record l O the said reed ansinitting r coil 35, conductors i 36 from whlch are attached thefinner 'endsot the i terminal posts 30 I"or outside Connection to e0 'Wilth'the ai; gaps37 (138 respectively lie-- twee the pan. of npperplates andloetweenv with. i. e

into the a'loi'esald passageway 1d the air" oscillates about the disk 1 as; (a torsional axis and movements Slllffi-tllefiufi upiand down therein anjdjthus change the .liux passing through the transmitting coil to induce; there :by currentsi l-niseld coil inaceorda ree a'lth the movements of theistylus as iis Swell understood, I

-Iclaim-zg i a r 1. An electrical transmitterfor; Vlphonographs, comprising-a closed casing-having an -openingtherethrough a magnet having separated cooperating pole pleces-extending over said fopening,.-.a transmitting, eoil 3 carried loy tliepole eees and hav a passage way therethrongh' eoaxial with the said casing opening and ;the gap-j.betiveenthepole pieces, a flexible inemhersecuredit'o'the cas- 111g over'its openlng-to seal the same areed of softiron fiXedlysecnredto the inner face of the flexible member vhich affords pivot therefor, said reed ex ending through the passageway of the transmitting; r coil and the said gap, and 'a stylus holderfixedly secured aid f being secured to vthe 3 :24 by a metal ring 42 I v V and the l radial slot l5'to accommo to'the outerfaeeof the fiexihleinember.

2. An electrical" trans nltter fer phonogi aphs, comprising a closed having an open n'g the ethroirgln a permanent il-shape magnet mjounted i-n the casing With separated pole pieeesat'its ends iandgextending over said opening, a transmitting coil carried-1h the pole pieees and having passageway therethreueh coaxial with the casing; ope v V g n between the pole niecesfafiete ible inenioer secured. to the casing over its opening to seal the same, reed oftsoftiron fixedly securedto theinner face of the flexible member-and extending throughthe passageway of the transmitting coil and the said gap, and a stylus holder fixedly secured to the outer face of the flexible member.

An electrical transmitter for phonographs, comprising a closed casing having an opening theretlirough, a magnet having separated cooperating pole pieces recessed at their outer ends and extending over said opening, a transmitting coil retained in the recesses of the pole pieces and, having a passageway 3 therethrough coaxial with the said casing 1 opening and the gap between the pole pieces, a flexible member secured to the casing over its opening to seal" the same, a reed of soft iron fixedly'secured to the lnner face of the flexible member and extending through the passageway of the transmitting coil and the said gap, and a stylus holder fixedly secured to the outer face of the flexible member.

4, An electrical transmitter for phonographs, comprising a closed casing having an opening therethrough, and an outlet for conductors, an insulation plug-sealing said outlet, terminal posts extending through the plug, a magnet having separated cooperating pole pieces extending over. said. opening, a transmitting coil carried by the pole pieces and having a passageway therethrough coaxial with the said casing opening and the gap betweenthe pole pieces, conductors connecting said transmitting coil with the said terminal posts, a flexible membersecured to theicasing over its opening to'seal the same, a reed of soft iron fixedly secured to the inner face of the flexible member and extending through the passageway of the transmitting coil and the said gap, and a stylus holder fixedly secured to the outer face of the flexible member. 7 p

5, An electrical transmitter for phonographs, comprising a closed casing having an opening therethrough, a magnet having separated cooperating pole'pieces extending over r, said opening, a transmitting coil carried by the pole pieces and having a passageway therethrough coaxial with the said casing opening and the gap between the pole pieces, a flexible member secured to the casing over its'opening to seal thesame, a reed of soft iron centrally secured to the inner, face of the ber.

flexible member and extending through the passageway of the transmitting coil and the said gap, and a stylus holder eccentrically secured to the outer face of theflexible mem- 6. An electrical transmitter for phonographs, comprising a closed casing having an opening therethrough and an outlet for conductors, an insulation plug sealing said outlet and terminal posts extending therethrough,

a magnet having separated cooperating pole pieces extending over saidopening, a transmitting coil carried by the pole pieces and having apassageway therethrough coaxial .with the said casing opening and the gap bethe casing to allow of filling the latter with a damping liquid.

In testimony whereof I aflix my signature. 1 LINCOLN THOMPSON. 

